The present invention relates to a laser scanner and a laser scanner measuring system for acquiring three-dimensional data by using GPS (Global Positioning System). The invention also relates to a target for calibration used for the laser scanner measuring system and relates to a calibration method for the laser scanner measuring system.
In recent years, with a widespread use of car navigation system and other related technique, there are increasing demands to have three-dimensional position data and further, three-dimensional image data, which can be used as map data. As a surveying instrument to acquire such type of three-dimensional data, a laser scanner measuring system using GPS and IMU (inertial measuring unit) is currently used. By using a laser scanner, it is possible to acquire an enormous amount of three-dimensional data within short time. Further, a position of the laser scanner is measured by using GPS and also a posture of the laser scanner is measured by using IMU. As a result, it is possible to acquire three-dimensional absolute coordinates on global surface.
In case where three-dimensional data of a construction or a building in urban space is acquired, a laser scanner, GPS, IMU, an image pickup device, etc. are on board of a mobile device such as a vehicle. While the vehicle is driven along a road, three-dimensional distance data on and around the road are acquired by using the laser scanner. Further, a position of the vehicle is measured by GPS at real time. As a result, three-dimensional absolute coordinates can be determined. Further, in parallel to these operations, images are acquired by the image pickup device, and by associating the images with the coordinates data, it is possible to acquire map data with images.
As described above, by using the laser scanner, a large amount of point group data (an aggregate of three-dimensional position coordinates data) can be collected in easier manner. On the other hand, it is very difficult to identify the measured points.
Also, the laser scanner has individual differences caused by error in a manufacturing process, and by error in a process of mounting. Further, when there is environmental change such as temperature change during a process of measurement, a measurement error may occur due to thermal expansion of the device or other causes. Therefore, it is very difficult to verify the measured data and to check an accuracy of the system. In particular, it is more difficult to verify the measured data and to check the accuracy of the system during the measuring operation.
JP-A-2000-194983 discloses a spatial data collecting device, which comprises a distance measuring device, a GPS, an IMU and an image pickup device, and which associates image information from the image pickup device with position information of place where the images are taken and/or road surface information of place where the images are taken, and wherein it is possible to intuitively identify condition of road and condition along the road. Also, a calibration method for calibrating a scanner is disclosed in JP-A-2005-55311, which measures an object to be measured with a known shape by a scanner device and carries out the calibration of the scanner based on a result of the measurement. Further, a surveying system using a laser scanner is described in JP-A-2008-82707.